(a) Field of the Invention
The present invention relates to a signal-adjusted LCD control unit and, more particularly, to an LCD control unit in an LCD device which is capable of being adjusted by software to conform to the γ-profile of the LCD panel in the LCD device.
(b) Description of the Related Art
Liquid crystal display (LCD) devices are increasingly used as display devices in a portable electronic equipment including a computer system, such as a mobile telephone. Among other LCD devices, the LCD device used in the mobile telephone is especially requested to have smaller dimensions and smaller weight.
FIG. 1 shows a conventional LCD device, which includes an LCD panel 60, an LCD driver 40 and an LCD controller 70. The LCD driver 40 is formed as a one-chip IC, mounted on the LCD panel 60 for driving the LCD panel 60. The LCD controller 70 is disposed separately from the LCD panel 60 and the LCD driver 40. The LCD controller 70 includes a γ-correction resistor string 71, an impedance converter 72, a voltage divider 73 and a Vcom-voltage generator 74.
Both the γ-correction resistor string 71 and the voltage divider 73 are connected between a high-voltage source line VCC and a low-voltage source line VSS to generate a plurality (n) of voltages and a plurality (m) of voltages, respectively. The impedance converter 72 converts the impedance of the plurality of voltages supplied from the taps of the γ-correction resistor string 71 to output a plurality of γ-correction voltages 103, which are fed to the LCD driver 40. Each signal line transferring one of the γ-correction voltages 103 is provided with a smoothing capacitor or bypass capacitor (not shown). The LCD driver 40 generates display voltage signals 108 based on the data signal 107 supplied outside from the LCD device and the γ-correction voltages 103, delivering the display data signal 108 to the data electrodes of the LCD panel 60.
The Vcom-voltage generator 74 generates a plurality of Vcom voltages 104 based on the voltages supplied from the voltage divider 73, the Vcom voltages 104 being supplied to the common electrode of the LCD panel 60. The LCD panel 60 is thus driven by the display data signals 108 and the Vcom voltages 104 based on an AC driving scheme to display on the screen thereof images including characters and pictures.
In the conventional LCD device as described above, the LCD driver 40 and the LCD controller 70 have different functions, and are generally disposed outside the LCD panel 60 separately from one another.
It is known that the LC layer of the LCD panel 60 exhibits a non-linearity of optical transmittance with respect to the display voltage signal applied therethrough. In view of this fact, the LCD driver 40 supplies specific display data signals 108, which are corrected based on the γ-correction voltages corresponding to the γ-profile of the optical transmittance of the LC layer, thereby effecting a suitable contrast on the screen of the LCD panel 60.
Otherwise, if a DC voltage is applied to the LC layer, an electro-chemical reaction arises on the surface of the electrodes of the LCD panel, whereby the lifetime of the LCD panel 60 will be significantly reduced. The AC driving scheme is such that the polarity of the drive voltage between the data electrodes and the common electrode is reversed at a constant cycle. The applied AC voltage, however, are often subjected to deformation of the waveform to cause an inequality in the waveform between the positive-polarity duration and the negative-polarity duration of the applied voltage. The inequality of the waveform in fact generates some DC component of the applied voltage signal, thereby causing an undesirable phenomenon such as flickering of the screen. The Vcom voltages as described above cancel the inequality of the waveform by changing the voltage level of the common electrode between both the durations, to thereby suppress the adverse effect by the DC component.
The γ-correction voltages and the Vcom voltages respectively have suitable values corresponding to the inherent characteristics of the respective LCD panels. This necessitates an initial adjustment of the γ-correction voltages and the Vcom voltages before the LCD panel is installed in service. The initial adjustment is generally conducted by a hardware work which determines the resistances of resistors of the γ-correction resistor string 71 and the voltage divider 73 provided as external resistors. In particular, the resolution of the γ-voltages generated by the γ-correction resistor string 71 is reduced after the adjustment by the external resistors, which necessitates incorporation of additional resistors to cancel the reduction of the resolution and thus complicates the work for the hardware adjustment.
In addition, the hardware adjustment of the LCD device especially increases the costs and the dimensions thereof due to the complicated structure of the LCD device including the LCD panel 60, LCD driver 40, the LCD controller 70 and the external members associated therewith.